1. Field of the Invention
This invention is directed to the cleaning of filter beds. More particularly, it is related to an improved process for cleaning a dry catalyst mass, such as used in a sulfuric acid plant or the like.
2. Description of the Prior Art
The catalyst mass or bed primary function is to enhance the reaction of SO.sub.2 to SO.sub.3. It is intended that all gases passing through the catalyst be free of all particulate matter, however, since no gas cleaning plant does a perfect job of particulate removal, some particles do reach the catalyst. Over a period of time, these particles build up in the catalyst and cause a resistance to gas flow which eventually leads to reduced flow rates and lower production of acid. In this event, such accumulation will prevent the efficient operation of the catalyst bed and thereby render it ineffective to perform its intended function. Accordingly, it, therefore, becomes necessary for the catalyst bed to be appropriately cleaned in such a manner as to render the bed once again effective for enhancing its cooperation with the gases which are being treated.
Heretofore known prior art methods for cleaning the catalyst bed ordinarily require that the catalyst mass and a layer of silicious aggregate material, which forms a portion of the catalyst bed, be removed from the tray upon which they normally rest. Subsequently, the aggregate which form the silicious layer and catalyst mass are screened and then reloaded onto the tray for later use. In some instances, however, after extensive use the catalyst mass and silicious layer are replaced with newer materials. One approach in the prior art has been to hand remove and screen the catalyst mass and silicious layer. This approach, however, is time consuming and costly. Another approach is to utilize a catalyst services contractor to remove, screen, and reload the catalyst mass as well as silicious layer back onto the tray. While utilization of a service contractor saves substantial time as compared with hand removal, this particular approach, nevertheless, also suffers similar shortcomings in that it is also relatively time consuming and expensive. Such approach, when used for a catalyst bed of 27,368 liters, for example, frequently requires an eight man shift to remove and screen the particulate matter of the catalyst mass. In addition, the downtime is about 70 hours.
Another shortcoming associated with such of the abovenoted prior art methods for screening the catalyst mass or aggregate, is that it is rather usual for at least 5% of the total catalyst mass to be lost through screening abrasion. As can be readily appreciated, the typical prior art approaches of cleaning catalyst filter beds of accumulated impurities is a rather time and labor consuming process, and one in which the filter bed is maintained out of useful operation for relatively long periods of time. Accordingly, such known techniques are expensive, especially when further considering the loss of time incurred because the catalyst bed is maintained out of normal operation.